Acetylation of Bcl6 and p53 in DLBCL lines after treatment with niacinamide and pan-class I/II DAC inhibitor. (A) Western blot analysis of Bcl6 and p53 in 6 untreated DLBCL cell lines. Bcl6 is expressed to a greater degree in GC- over ABC-subtype DLBCL. (B) Acetylation of Bcl6 in 2 GC-derived DLBCL cell lines treated for 3 hours with niacinamide (N), 10 mM, and/or 1 of 4 pan-class DAC inhibitors: vorinostat (V), 3 uM; panobinostat (P), 15 nM; belinostat (B), 600 nM; or romidepsin (R), 6 nM for OCI-Ly1 and 1.5 nM for OCI-Ly7. Whole cell lysates were analyzed by immunoprecipitation for Bcl6 and Western blot analysis for acetyl lysine. Densitometry analysis was performed on scanned immunoblot images using the ImageJ software (National Institutes of Health). Relative levels of acetylated-Bcl6 were calculated and plotted. (C) Western blot analysis of acetylated-p53, total p53, p21, and Blimp1 in 4 DLBCL cell lines treated with 10 mM niacinamide, 1.5 nM romidepsin, or the combination for 24 hours. OCI-Ly7 does not express p21 at measurable levels at baseline.